This invention relates to motor graders and more particularly to the improved control of the working implement or blade of a motor grader.
The working implement such as a blade or moldboard of a motor grader is conventionally mounted for a variety of adjustments in position relative to the frame in order to meet the requirements of each particular job which the motor grader is to perform. Thus, the working implement is mounted for elevational adjustment, cross-slope adjustment, lateral sliding adjustment, and rotational adjustment. The working implement is mounted on the main frame of the motor grader by means of a drawbar frame in order to provide for elevational adjustment and cross-slope adjustment and the working implement is mounted on the drawbar frame by means of a "circle gear" in the form of a ring-like structure rotatably mounted on the drawbar frame in order to provide for rotational adjustment with the lateral sliding adjustment being provided by the means which mounts the working implement on the circle gear. Preferably, the circle gear is locked in position with respect to the drawbar frame when it is not being rotated in order to prevent stress in the drive train thereto.
However, it has not been possible, according to the teaching of the prior art, to lock the elevational position of the working implement. In the first place, the rotatable mounting of the circle gear must be sufficiently loose when not locked against rotational adjustment to enable the desired rotational adjustment to be achieved. More importantly, the circle gear and its bearing support are peculiarly subject to wear during operation resulting in a further loosening of the fit therebetween and consequent elevational instability. Finally, the locks or brakes that have been used according to the teaching of the prior art have tended to result in elevational movement of the circle gear, when they are released or applied, through a distance approximating the amount of wear or looseness in the fit between the circle gear and its rotatable mounting means.
Modern motor graders use an automatic blade control device for reading the desired level from a reference grade line or wire and automatically adjusting the elevational position of the working implement in an attempt to maintain the reference level. However, such devices cannot compensate for changes in the elevational positioning of the working implement due to wear in the mating surfaces of the rotatable mounting means and any changes in the elevational positioning of the working implement which may occur during rotational adjustment of the working implement will result in departures from the reference grade level. Since tolerances as small as 1/8 inch (3.175 mm.) are now required in road grading operations, it will be seen that departures from the reference grade level during rotational adjustment of the working implement due to the wear inherent in the mounting structures or movement resulting from the operation of locking or braking devices to prevent rotational movement would be highly undesirable in such close tolerance work.
It is a primary object of this invention to provide an improved control for the working implement or blade of a motor grader or the like which will insure a consistent pre-selected elevational adjustment of the working implement at all times and particularly during rotational adjustment of the working implement.